Bio-oils are complex microemulsions of aqueous and non-aqueous phases containing hundreds of different organic and inorganic compounds. Oxygenated hydrocarbons in bio-oils include esters, acids, aldehydes, alcohols, ketones, sugars, and various phenol derivatives. These reactive species in bio-oils complicate storage, transportation, and downstream processing because secondary reactions cause condensation and polymerization reactions which increase the viscosity of the bio-oil and form problematic solids. Bio-oils are also corrosive due to the presence of organic acids such as acetic acid and formic acid as well as phenolics that can damage the infrastructure of conventional processing systems. Bio-oils must therefore be upgraded before they can be introduced into fuel processing systems for processing into transportation fuels. Reactivity and lack of stability of bio-oils are well-known problems. These problems are attributed to reactions involving acids, aldehydes, sugars, and phenols. For example, organic acids can form esters by reaction with alcohols or olefins, can catalyze condensation reactions, and can cause corrosion. Aldehydes can oligomerize or react with phenols to form resins. Removal of these reactive functionalities can thus improve bio-oil stability. Stabilization of bio-oils by hydrogenation is typically performed using pressurized H2 at elevated temperatures. However, bio-oils lack thermal stability. And, upon break down, compounds in bio-oils form coke which blocks catalyst sites and plugs reactors during treatment at elevated temperatures. These issues have yet to be resolved.
Accordingly, new systems, processes, and catalysts are needed to upgrade bio-oils under mild conditions, to reduce reactive functionalities to more stable compounds, to reduce corrosivity of the bio-oil, and to increase carbon and hydrogen efficiency of bio-oil processing, e.g., into bio-based transportation fuels. The present invention addresses these needs.